Shale distillation



W. W. ODELL SHALE DISTILLTION Feb. 19, 1952 Filed Nov. l, 1946 MEZ di 54ML@ uw /mm ....zmanm Nm Owl...

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I* mao. Mui eMG dmmumu Nm @v oq duk/#m1 JvLLL'am-CJ-TOce i averzbor -/QQ/Wwuabbomag dMQOI Patented Feb. 19, 1952 SHALE DISTILLATION William W. Odell, Washington, D. C., asslrnor to Standard Oil Development Company, a corporation of Delaware Application November 1l 1946, Serlal No. 707,085

3 Claims. l

The present invention relates to the production of hydrocarbon oils and, more particularly. to the art of treating bituminous materials such as oil shale, tar sands, coal and the like in a continuous procedure to recover therefrom valuable hydrocarbons including fuels for internal combustion engines, heating and fuel oils, etc.

Continuous processes for the distillation of oilbearing or oil-forming minerals are known in the art. For example, it has been suggested to suspend powdered shale in gases and to pass the suspension continuously through successive distillation zones operating at increasing temperatures while regrinding the shale between stages to prevent overheating and cracking of occluded distillable shale constituents. Aside from the expense and complications resulting from the multiple grinding stages in this procedure, the heating of the suspended shale particles is irregular and the carbonaceous shale constituents are incompletely utilized in kkthe process, leading to process ineilciencies and low yields.

Other continuous prior art processes carry out the distillation of oil-bearing minerals in the form of dense turbulent beds of finely divided solids fluidized by upwardly flowing gases while generating the heat required for distillation by burning combustible shale constituents within or outside the distillation zone and supplying sensible heat of solid and/or gaseous combustion products to the distillation zone. 'I'hese processes frequently involve appreciable losses of valuable distillation products by the heat-generating combustion and dilution of the product vapors with worthless nue gases or they require circulation of large amounts of heat-carrying solids.

The present invention overcomes the aforementioned diiculties and affords various additional advantages as will appear from the 'following description read with reference to the accompanying drawing.

It is, therefore, the principal object of the present invention to provide improved means for distilling oil-bearing minerals in a continuous procedure.

Another object of my invention is to provide improved means for continuously distilling oil-bearing minerals without appreciable losses by cracking and/or combustion of valuable volatile products and with full utilization of the carbonaceous constituents of the charge,

Other and more specific objects and advantages will appear hereinafter.

In accordance with the present invention, oll- 2 bearing minerals of a fluidlzable particle size are fluidized by a carrier gas, the iluidized mixture is passed at a relatively high linear velocity through an externally heated heating zone to attain distillation temperature and is thence discharged into a iluidlzed soaking zone wherein the distillation is completed and distillate vapors are separated from spent solids. The coke of the distillation residue is converted with steam and/or free oxygen-containing gas in a preferably luidized state in a gasification zone into a fuel gas at least a portion of which is burned to supply the heat required in the heating zone. In this manner, the solid particles to be distilled may be initially heated uniformly to optimum distillation temperatures or to a temperature approaching optimum by external application of heat without appreciable cracking of reaction products. No valuable volatile products are burned and the carbonaceous constituents of the charge are largely recovered or fully utilized in the process without requiring circulation of heat-carrying solids. As a. result, the process economies and yields are considerably improved.

A further appreciable increase in the yield of valuable volatile products may be obtained by using the light ends of the product distillate in a recycle fashion to fluidize the charge supplied to the heating zone. In this manner, the carrier gas flowing through the system will be saturated with condensable low-molecular weight hydrocarbons during the starting period of the process.

It is preferable that the uidized solids charge be passed upwardly through the heating zone in order to maintain proper uidization and suspension densities of the order of 1 20 lbs. per cu. ft. at which the excellent heat distribution of iluidized-solids masses may be combined with relatively small diiferentials between the linear flow velocities of the gaseous and solid constituents of the fiuidized mass which may fall within the approximate range of 1-10 ft. per second. Thus, the oil-bearing solids charge may be heated to a temperature approaching the desired distillation temperatures of about 300-550 C. within relatively short heating times of about 10 to 60 seconds or more as desired. A heating coil of suitable length and diameter has been found to be most useful for this purpose.

One of the advantages of this process is that the duration of this preheating period is controllable to suit the characteristics of any particular material to be treated. The major variables affecting the optimum duration of the latter period are:

(a) Temperature in the furnace atmosphere adjacent the transfer coil.

(b) Temperature and amount of radiant surface adjacent the coil.

(c) Length of the heating coil.

(d) Diameter of the coil.

(e) Velocity of flow of the solids being treated in the coil.

(f) Temperature of the solids initially charge to said coil.

(y) Temperature of the fluid carrying agentv as initially charged.

(h) The amount of oxidation promoted during passage through the coil.

(i) The moisture content of the charged solids.

(i) The amount of fuel burned in the heating furnace.

(k) The heat capacity of the solids treated.

(l) Size of particles of the solids treated.

Thus if a steel coil 8 inches in diameter and 110 ft. long is heated in a furnace in which suiiicient fuelis burned to give a furnace temperature above 1800 F. and the fluidized solids, oil shale for example, is introduced into the coil at a linear velocity of 1 ft. per second, the time of heating (duration of the preheating period) is approximately 110 seconds and, under the particular conditions of furnace design, the shale is preheated to the desired temperature without internal heating such as internal combustion, with recirculated product gases as transporting agent, and with the solids having a size of 1/8 in. and smaller. To increase the duration of the heating period it is only necessary to decrease the rate of feed of said solids; and to increase the temperature either the furnace temperature is raised, the duration of heating period increased. internal combustion promoted, circulating gas is preheated or combinations of these variations are effected. With solids of high moisture content, these expedients may be used or the diameter of the coil tube may be decreased whereby the surface-volume ratio is increased. This control over the duration of the preheating period permits the ne adjustment by which the maximum or optimum yield of valuable products is obtained.

Distillation begins in the heating zone and is completed in the fluidized mass in the soaking zone at linear velocities of the upwardly flowing fluidizing gas of about 0.1- ft. per second and bed densities of about 10-30 lbs. per cu. ft., favoring perfect heat distribution and constancy of temperature resulting in rapid and complete evolution of distillable constituents of the charge within short residence times of about 10 to 60 seconds, more or less, according to the size of particles in process, temperature of the iiuidizing gas and the amount of combustion promoted in the soaking zone, which time is insuiiicient to permit an undesirable amount of cracking of valuable distillate vapors even at distillation temperatures of about 600-1000 F.

Carbon-containing residues are withdrawn downwardly from the fiuidized bed of the soaking zone and, if desired after stripping with steam or the like. subjected to gasification without appreciable heat loss. The fuel gas produced is burned in the heater with air in contact with the walls of the heating zone to supply the heat for preheating.

Product vapors are withdrawn overhead from the fiuidized bed of the treating zone, separated from suspended solids and subjected to fractionation to recover liquid products of various boiling ranges and gases. The latter are preferably used to propel the charge through the system as indicated above.

Having set forth its general nature and objects, my invention will be best understood from the more detailed description hereinafter in which reference will be made to the drawing which is a semi-diagrammatical illustration of a system adapted to carry out preferred embodiments of my invention.

Referring now to the drawing, the system shown therein essentially comprises a solids feed hopper a heater 20, a soaker 30, a gas generator anda fractionator "ID, the functions and cooperation of which will be presently explained using the distillation of oil shale as an example. It will be understood, however, that other carbonizable solids may be employed in a substantially analogous manner.

In operation, raw shale ground to a uidizable particle size of about 1/8" diameter to 200 mesh is passed from the feed hopper I through a standpipe 3 or the like, into feed pipe l. The flow of solids through standpipe 3 may be facilitated by the injection of small amounts of an aerating gas such as steam or product gas through one or more taps 5.

Feed pipe 'I receives gas such as product gas, steam, and/or combustion-supporting gas for uidization and propulsion from conduit 9 which is preferably provided with an ejector I0 to secure good mixing and fiuidization. Product gas, which is my preferred iiuidizing and propellant gas, may be supplied through pipe II by pump I2, or, if desired, via line I3, preheating coil I4 and line I5, to attain a preheat temperature of about 200-550 C. Steam may be fed from line lI'l and combustion-supporting gas such as air and/or oxygen from blower I8 through pipe I9. An amount of about 4 to 25 standard cu. ft. of fluidizing gas per lb. of shale charged is generally suitable to convert the shale into a iiuidized mass of this type which iiows like a liquid through pipes and ducts.

The -fluidized solids enter heater 20 through coil 22 in which they flow upwardly propelled by the gas supplied from line 9. Heater 20 is maintained at a chosen temperature above about 500 to 1000 C., and may advantageously be maintained appreciably higher by the combustion of fuel gas supplied through line 24 as will appear more clearly hereinafter. If desired, additional combustible gas may be supplied to heater 20 in the form of product gas fed by pump I2 through lines I3 and 25. Additional heat may also be generated by supplying small amounts of air and/or oxygen through line I9, preferably in combination with a supply of product gas through line II, in order to support a limited heat-generating combustion within coil 22. Combustion air enters heater 20 through line 26 and flue gases are withdrawn through line 21 to be vented or used to preheat process gases and/or solids.

The nuidized solids being preheated pass through heating coil 22 at a linear velocity of about 1 to 10 ft. per second or more to establish an apparent solids density within coil 22 of about 8 to 20 lbs. per cu. ft. The dimensions of heater 20 and coil 22 are so chosen that the solids charge, when leaving coil 22, has attained an optimum distillation temperature usually within the range of 300 to 550 C. or the residence time in coil 22 is chosen, other factors remaining the same,

so that the optimum discharge temperature prevails.

The preheated iluidized shale together with the iiuidizing gas and such distillate vapors as have been liberated in coil 22 enters the lower portion of the substantially cylindrical soaker 30 through line 28. Soaker 30, the cylindrical main section of which has a cross-section substantially larger than that of coil 22, is preferably provided with a conical bottom portion 32 and a perforated distributing plate such as grid 34 arranged above the discharge end of pipe 28.

A fiuidizing gas which is preferably product gas preheated in coil I4 at least to the desired distillation temperature is supplied from line l5 via lines 36 and 38 to the bottom portion 32 of soaker 30. The amount and linear velocity of this iiuidizing gas are so chosen that the linear velocity of the gas and vapors flowing upwardly through the bed in the upper portion of the cylindrical main section of soaker 36 falls within the approximate limits of 0.3-6.0 ft. per second at which the mass of shale undergoing distillation in soaker 30 takes on the form of a dense. turbulent, ebullient bed of solids having a Well defined upper level L30 and an apparent density of about l0 to 25 lbs. per cu. ft.

If desired, a small amount of a combustionsupporting gas such as air and/or oxygen may be supplied to soaker 36 through line 39 to add more heat to the distilling shale by a limited combustion of some of the fixed carbon in the residue shale and to maintain the distillation temperature at or preferably slightly above the temperature at the outlet of coil 22. About l0 a, well defined upper 1eve1 L50, in a manner simto lbs. of oxygen per ton of shale to be distilled is generally suiiicient to maintain temperatures of about 450-600 C. in soaker 30; that amount of oxygen will provide a boost in the temperature of the shale above that at the coil discharge amounting to approximately to 50 C.

In accordance with a preferred embodiment of the invention, some spent shale is permitted to remain as an accumulated non-iluidized mass at the base of soaker adjacent the discharge end of pipe 39 in order to prevent withdrawal of incompletely treated shale. This may be accomplished by arranging a grate 34A with proper space openings below grid upward gas flow through the openings of grate 34A so as to permit downward circulation of shale residue through these openings. In this manner, the air introduced through line 39 will generate heat by burning the carbon of the shale residue rather than reaction products.

When the velocity of flow of gaseous fluids is so proportioned, by regulating valves 38 and 38A, it is possible to maintain a more dense portion of the bed just above the grid 34A than at a higher level. This condition favors the downward passage of the residue shale through 34A into the bottom of the soaker at a rate controlled by adjusting valves 38 and 38A; the greater the relative amount of fluid flowing through 38 the less the diierential in density in the bed and the lower the rate of travel of solids downward through 34A and vice versa. However, it will be understood that instead of withdrawing solids from the soaker in this manner, from a settled mass, they may be withdrawn in the customary manner by extending oitake 46 up into the fluidized bed above grid 34A. This latter procedure is advantageous when employing a deep bed and when it is desirable to take advantage of the 34 and controlling the pipe 40 of soaker 30.

pseudo-hydrostatic head of the fluidized bed in soaker 30 in promoting circulation of solids therefrom. y

Fluidized shale residue is withdrawn downwardly from section 32 of soaker 30 through standpipe 40, if desired, under the pseudo-hydrostatic pressure of the iluidized solids bed in soaker 30. Standpipe 40 is provided with a contro.' valve 42 which regulates the rate of solids Withdrawal through pipe 40 and thus the residence time of the shale in soaker 36. A residence time of less than 2 minutes is generally sufficient for a substantially complete distillation of distillable shale constituents. The solids ilowing through are aerated and, if desired, stripped oi adhering hydrocarbon vapors by steam added through one or more taps 4|.

Shale passing through valve 42 is picked up in line 44 by a propelling gas such as steam, air and/or oxygen supplied through line 43. This gas is preferably preheated in heat exchange with hot ilue gases withdrawn through line 21 from heater 20. The suspension of treated shale in hot propelling gas may be heated in line 44 by a .partial combustion of its carbon content to temperatures of about 600-1000 C. and passed through line 46 directly to fuel gas generator 50 in which it forms above grid 52 a dense turbulent mass of solids iiuidized by the gaseous gasifying medium such as steam and/or air which may be preheated by maintaining some hot spent shale in the lower portion of generator to be rst contacted by the gasifying medium and which is supplied below grid 52 through line 54 to form ilar to that outlined in connection with soaker 30.

If desired, the shale flowing through line 44 may be passed through line 48 to a receiverstripper 56 having a construction similar to that The shale is maintained in vessel 56 as a uidized mass above grid 58, uidizing and stripping steam being supplied through line 50 preferably after preheating to about 400 C. in heat exchange with flue gases from heater 20. Steam and stripped hydrocarbons leave receiver 56 overhead from level Las through line 62, are separated from suspended solids in a conventional gas solids separator such as cyclone 64 and passed through line 66 to the bottom portion of fractionator 10. Solids separated in separator 64 may be returned to receiver 56 through line 65. A desirable modification of this procedure comprises the quenching of the vapors in separator 64 by water injected through line 61. This water vaporizes in separator 64 and condenses together with the stripping steam in the bottom of fractionator 10 to form an aqueous sludge containing solids nes which may be withdrawn from the bottom of fractionator 10 through line 12 without appreciable loss of valuable hydrocarbons.

Stripped fluidized shale passes downwardly from receiver 56 through a conventional aerated standpipe 51 to gas generator 50. The solids entering gas generator 50 through lines 46 and/or 51 are at a temperature appreciably above ignition temperature which is suilciently high to initiate the producer or water gas reactions. The amounts of steam and/or air supplied through line 54 and the shale residence time controlled by the withdrawal of solid gasification residue through aerated standpipe 53 provided with control -valve 55 are so chosen that the carbon of the shale residue is substantially completely converted into a fuel gas rich in CO and H2 at temperatures oi about 900-1100 C., but preferably below the fusion point of the shale ash. In general, the amounts of oxygen and steam used in gasiiying the carbon in the shale residue in generator 50 are adjusted in accordance with the carbon content of said shale residue; the relative amounts used are regulated to keep the temperature below ash softening temperature. The solid gasification residue withdrawn through pipe 53 may be discarded, if desired, after a suitable heat exchange with solid and/or gaseous process materials in a conventional manner.

In place of a conventional gas-solids separator such as cyclone 64, gas generator 50 may be provided with an enlarged upper section 59 wherein the gas velocity is sufliciently reduced to permit substantial sedimentation of entrained solids iines. It is noted, however, that small proportions of entrained solids iines will increase the heat capacity of the heating medium in heater 2U so that solids separation in 59 need not be quantitative.

The fuel gas produced in generator 50 passes substantially at the temperature of generator 50 through line 24 to heater 20 to be burned therein to produce the heat required for shale distillation as described above. Any excess amount o! fuel gas may be withdrawn from line 24 through branch pipe 41 for any desired use, for instance as feed gas for the catalytic synthesis of hydrocarbons from carbon monoxide and hydrogen.

Returning now to soaker 3l) distillate vapors and gases admixed with iluidizing and possibly small amounts of flue gases leave overhead from level les through line 3l and enter a conventional gas solids separator 33 from which solids may be returned through pipe 35 to soaker 20 or discarded through pipe 31. If desired, solids return line 35 may be used as a reheater by introducing superheated steam and/or a combustion-supporting gas such as air through taps 45 to reheat the solids in line 35, for instance by a heat generating combustion of their carbonaceous constituents so as to supply additional heat to soaker 30.

Product vapors and gases, now substantially free of entrained solids pass through line 49 to a middle section of conventional fractionator from which 3 or more hydrocarbon oil fractions oi diierent boiling range may be recovered through draw-oil pipes 14, 16, and 18. Gaseous f overhead leaves fractionator 10 through line 80.

At least a substantial portion of the overhead gases is passed through line 82 to condenser 84 wherein condensable fractions are separated and withdrawn through line 85. The gas leaves condenser 84 through line 86 under the suction of pump i2 to be distributed through lines Il, I3, I4, and 38 as described above. Any excess product gas may be withdrawn from the system through line 8l.

The optimum conditions for operating the system illustrated by the drawing exist when the amount of fuel gas used in heater 20 ls less than the total amount of gas produced in the process. when the gas supplied with the shale to coil 22 is preheated, when the amount of combustion-supporting gas supplied to coil 22 and soaker 33 is suflicient only to generate heat enough to raise the temperature of the shale in 22 so that it discharges into soaker at a temperature of about 300-540 C. and to generate enough heat by combustion reactions in soaker 30 so that the shale therein is heated not appreciably above 550 C.

While I have shown aerated standplpes 3, 4U, 53 and 51 to be used for the withdrawal of fiuidized solids from vessels I, 30, 50 and 56 it should be understood that other conventional means for conveying uidized solids may be used instead, such as mechanical conveyors or the like. My process may be operated in a fully continuous manner by continuously feeding process solids and gases and continuously withdrawing spent shale and distillation products. Other modifications Within the spirit of my invention may occur to those skilled in the art.

My invention will be further illustrated by the following specic example.

Example The operating conditions and yield data given below refer to the distillation of a Green River oil shale crushed to 11g in. and iiner in accordance with the present invention.

Temperature of shale charged C 30 Internal diameter of coil in-- 2 Length of coil ft 108 Duration of heating period in coil (approx.)

sec-- 60 Temperature of shale discharged from coil C 466 Steam supplied to coil per hour (approx.)

lbs 10 Stripped shale gas supplied to coil per hour cu. ft 260 Air to coil None Temperature of shale discharged from coil to soaker C 466 Area of cross-section of soaker (approx.)

sq. ft-- 0.6 Inside diameter ft-- 1.0 Depth of bed in soaker do 5.0 Maximum temperature attained in soaker C 530 Air supplied to soaker per ton raw shale treated cu. ft 890 Steam supplied to soaker per ton raw shale treated lbs 5+ Hot shale gas supplied to soaker additional to that from the coil per ton of shale cu. ft-- 300 Shale residence time in soaker min 1 Yields:

Oil recovered per ton of shale charged gal 33.10 Light oil recovered from gases by scrubhing per ton of shale charged gal 0.87 Total liquid products per ton of shale charged gal 33.97 Specic gravity of the condensed oil 0.900

Gas after condensation and scrubbing cu. ft. per ton of shale 1,780

Composition of gas at soaker offtake after condensing and scrubbing out light oil:

Per cent by Volume CO2-l-H2S 15.0 Illuminants 3.4 CO 3.5 H2 20.7 CH4 9.3 C21-Ie 8.4 N: 39.7

Carbon content of the treated shale as discharged from soaker weight per cent-- 6.6 Carbon per ton of raw shale lbs 105.6

Conversion of lbs. of this carbon to producer gas at 60% eiciency will yield 783,000 B. t. u.

aseaos This is suiiicient to operate the process when good furnace efficiencies are obtained. In the foregoing example the heat required in the soaker was largely supplied by burning some of the shale gas in the soaker. The soaker may have a number of horizontal grids spaced at an equal distance along its length to prevent uneven ow and uneven uidization in the shale in process. Under these conditions, there is a maximum possible shale residence time in the soaker which is approximately 224 seconds; however, it may be and preferably is less. The rate of feed of fresh shale to the coil determines the rate of feed to the soaker, and in order to provide a longer residence time in the soaker, larger diameter and/or a deeper bed in the soaker is required. With a larger diameter it may be necessary to circulate more gas, air or steam or combinations of them in order to maintain the solids in the soaker in a fluidized state; the amounts of iluidizing gases necessary depend on the size and density of the shale particles as they are fed to the soaker. These particles may be much smaller than those fed to the coil due to disintegration, hence it is necessary to adjust conditions to the characteristics of the material treated.

Shale oil begins to be evolved from shale at about 350 C., hence the relative amount of pyrolysis conducted in the coil can be regulated by controlling temperature. In other words, the coil may be used to heat the raw shale to about 350 C. and thus increase its capacity and the rest of the processing may be carried out in the soaker using hot recirculated gas with selected amounts of air, steam, producer gas or combinations of these. Sufficient gasiform material is supplied to the soaker to maintain a fluidized bed therein.

When anthracite coal fines are treated for the production of gas of high hydrogen content, a higher temperature may be employed in the coil. The total yield of volatile hydrogen may be as high as 9,000 cu. ft. per ton. When using low cost fuel such as culm anthracite, it is possible to economically produce hydrogen by heat treating the anthracite as in coil 22 of the drawing and when carbon monoxide is also desired a gas containing free oxygen is introduced into coil 22 through I9 and 9 and is also introduced in amounts desired into the soaker 30. As in the case of shale treating, the hot residue from the soaker is adapted for use in making producer gas.

Fuels of high ash content may be treated in this manner as well as lignite, bituminous and other coals. However, when lignite, which contains 40% of water as mined, is employed it is sometimes preferable to eliminate much of this moisture by drying prior to the distillation treatment. When the raw lignite containing an appreciable amount of moisture is treated as described for oil shale, the moisture forms steam in the coil which is useful in the process; thus the coil functions, in this instance, as a boiler and preheater. The preheated lignite along with the generated steam passes into the soaker and is either further heated therein for distillation products or at higher temperature in the presence of oxygen for the information of CO and Ha. In the latter case, much of the steam for gas fication is furnished by the natural moisture cor tent of the fuel being processed.

It will be noted in the case of lignite, brown coal and sub-bituminous coals that the vapors evolved in heating up to about 350 C. comprise largely H2O and CO2 both of which react with carbon by the well known water gas reactions at higher temperatures. The temperature in the fluidized bed in the soaker should be 900 C. to 1010D C. and could be higher for this purpose. The soaker may be designed for treating coal so that the residence time of the coal y in the soaker is suiiicient to permit the desired amount oi gasification.

Certain oil shales and coals disintegrate to very minute size particles by explosive force when the small-size particles are rapidly heated such as by suddenly introducing them into a hot fluidized bed of solids. This effect is very appreciably reduced when the material to be treated is preheated at a controlled rate as described, before injecting it into such a bed. This is an important advantage of the present invention.

The foregoing description and exemplary operations have served to illustrate specic applications and results of my invention. However, other modifications obvious to those skilled in the art are within the scope of my invention. Only such limitations should be imposed on the invention as are indicated in the appended claims.

I claim:

1. In the process of producing hydrocarbons from carbonizable minerals by preheating and distilling said minerals at a carbonization temperature in the form of subdivided uidized solids, the improvement which comprises passing the entire charge of fresh carbonizable minerals as an extended confined stream of fluidized subdivided solids, said stream having an apparent density of about 1-20 lbs. per cu. ft.. upwardly through a heating zone, externally heating said stream to a temperature of from about 30G-550 C. during a time period oi' from 10-60 seconds, passing the heated carbonizable minerals from an upper portion of said stream into an enlarged distillation zone, maintaining said carbonizable minerals in said distillation zone in the form of a dense turbulent fluidized bed having an apparent density of about 10-30 lbs. per cu. ft., maintaining a stripping zone directly beneath and in open communication with said distillation zone, passing a hot gas into said stripping zone and thereafter into said distillation zone to maintain the latter zone at temperatures of from about 25-50 C. above those prevailing in said confined stream. maintaining the carbonizable minerals in said distillation zone for a period of time of from about 10-60 seconds, but for an insufficient time period to cause substantial cracking of volatile distillation products, withdrawing solids distillation residue from a lower point of said distillation zone, passing said solids residue into said stripping zone. passing said residue in nonfluidized form downwardly through said stripping zone countercurrent to said upwardly moving hot gas whereby volatile material is stripped from said solids residue and recovering for product, volatile distillation products from an upper point ofsaid distillation zone.

2. 'Ihe process set forth in claim 1 in which a fuel gas produced by said carbonization is burned in heat exchange relationship with said confined stream to preheat the solids therein.

3. 'I'he method set forth in claim 1 in which the said hot gas introduced into the stripping zone to supply additional heat to the distillation zone and to strip the distillation residue is formed by introducing a fuel gas produced in the distillation and burning the said fuel gas in the presence of added oxygen-containing gas.

REFERENCES CITED 5 The following references are of record in the me of this patent:

UNITED STATES PATENTS Number Name Date 1,396,173 Fenton Nov. 8, 1921 1,538,954 Rosenthal May 26, 1925 1,732,219 Bjerregoard Oct. 22, 1929 1,950,558 Karrick Mar. 13, 1934 2,285,276 Hemminger June 2, 1942 15 WILLIAM W. ODELL.

Number Number Name Date Kuhl Jan. 25, 1944 Alther Feb. 12, 1946 Blending Mar. 5, 1946 Day Sept. 3, 1946 Egloi Jan. 21, 1947 Barr Dec. 9, 1947 Jewell Apr. 20, 1948 Peck Sept. 21, 1948 Peck Aug. 30, 1949 FOREIGN PATENTS Country Date Great Britain Dec. 13, 1928 

